1. Field of the Invention
This invention pertains generally to a device for analyzing a sample and more specifically to a device for performing long-pathlength capillary spectroscopy on a sample.
2. Description of the Related Art
Capillary spectroscopy is frequently used in the analysis of small-volume liquid samples. Traditionally, optical spectroscopy of samples in capillary tubes has been achieved by using simple lenses to excite the sample and collect the resulting signal of interest, FIG. 1a. More recently, these standard optical arrangements have been replaced with fiber-optics, FIG. 1b. Coupling of a fiber-optic probe to the end of a capillary tube has provided a much simpler means of sample excitation and signal collection. In addition, this arrangement has allowed for the excited and collected light to be efficiently waveguided throughout the sample medium over a long pathlength. Thus, a larger sample is interrogated (opposed to traditional capillary or non-capillary measurements) and significant signal enhancements have been achieved.
While the advantages of long-pathlength capillary spectroscopy are noteworthy, the technique has often been underutilized due to the expense, complexity and time requirements associated with current technologies. To date, these methods employ two distinct steps. First, the capillary is filled using one of several techniques, and second, the capillary is coupled to a fiber-optic probe for spectroscopic analysis. Disadvantages for each of these steps (in the current form) are as shown below.
The filling of long-pathlength capillaries is typically achieved via pressure delivery systems, mechanical pumps or capillary submersion. Pressure delivery and mechanical pumping can be expensive and require a significant amount of equipment, maintenance and overhead. Capillary submersion is comparatively inexpensive but requires a large amount of sample. This is an option that often does not exist and contradicts the logic of employing capillary spectroscopy in the first place.
After the capillary is filled it is coupled to a fiber probe for spectroscopic analysis. Because considerable alignment is required prior to each run, the time required to sample numerous analytes of interest can become impractical. Furthermore, the optimization of such alignments can vary from one sample to the next, making the comparison of a series of measurements difficult. Such alignment problems can be avoided by permanently coupling the probe and capillary, however, it becomes difficult to flush the system between samples. This can result in residual contaminants being left behind and can adversely effect the results of subsequent measurements.